The present invention relates to a fuel cell and, more particularly, to a differential-pressure control device for a fuel cell which is arranged to effect control of the differential pressure between electrodes of the fuel cell.
The differential pressure between electrodes of a fuel cell has hitherto been controlled by adjustment of the valves shown in FIG. 1. In FIG. 1, the reference numeral 1 denotes an anode of a fuel cell, the reference numeral 2 a cathode, and the reference numeral 3 a cell container. The flow rates of gases allowed to flow into the electrodes 1, 2 and cell container 3 are respectively controlled, in response to the variation in load of the cell, by flow control valves 4, 5 and 6 provided at the side of gas inlet. The difference in pressure between the anode 1 and cathode 2 is detected by a differential pressure gauge 7 and is controlled by driving a differential pressure control valve 8 with the use of a deviation between the value of detection and a predetermined set value.
Similarly, the difference in pressure between the cathode 2 and the cell container 3 is controlled by means of a differential pressure control valve 10, and the pressure of the cell container 3 is maintained to be constant by a pressure control valve 12. The gases which have passed through the differential pressure control valves 8, 10 and 12 respectively, join each other at the downstream side of an external heat portion 13 of a fuel improvement device for fuel cell. Since this manner of controlling the differential pressure between the electrodes of the fuel cell uses the valves having movable parts, it has drawbacks. So countermeasures are required to be taken against a defective operation due to deterioration of such movable parts with the lapse of time, a non-uniform operation due to the variation in characteristic of the valves, and a possible danger which arises from the use of combustible gas due to the use of electric signals.
Further, since the above-mentioned manner of controlling the differential pressure between the electrodes of the fuel cell uses the valves having the movable parts, it is limited in respect of the control performance, i.e., it poses the problem that its control system cannot sufficiently respond to the small and transient variations in pressure of the inflow gas.
Solutions to the latter problem are disclosed in Japanese Pat. "Kokai" No. 164159/83 and Japanese Pat. "Kokai" No. 165269/83. What is disclosed in Japanese Pat. "Kokai" No. 164159/83 is a device prepared by connecting a means comprised of a tank and a water seal equipment in parallel to a fuel gas supply pipe line. This device is arranged such that, when the pressure of the fuel gas is minutely varied, the liquid level of the water seal equipment rises or falls in accordance with the pressure variation. The volume of a fuel gas pipe line increases or decreases due to the rise or fall of the liquid level in accordance with the pressure variation, whereby this transient variation in pressure is absorbed.
The device disclosed in Japanese Pat. "Kokai" No. 165269/83 includes the first and the second sealing means, each of which is arranged to seal a communication passage between two gas chambers communicated with each other at their bottom regions with a sealing liquid having a free surface, and one of gas chambers of the first sealing means and one of gas chambers of the second sealing means are respectively connected in parallel to a fuel gas line and an air line of the inlet side of the fuel cell and the other gas chambers of the first and the second sealing means are connected to an inert gas line of which pressure is set at a predetermined pressure level. In this device, when the pressure of the fuel gas or air varies transiently, the liquid level of the liquid sealing means varies in accordance with the variation in the differential pressure between the inert gas, which serves as a reference pressure, and the fuel gas or air, whereby the gas occupied volume of the gas chamber is increased or decreased so as to absorb the transient small variation in pressure.
The above-mentioned two devices are each intended to absorb the above-mentioned transient small variation in pressure of the fuel gas or air but, in each device, the continuous differential pressure between the electrodes of the cell must be controlled by the differential pressure control valves. Therefore, the above-mentioned drawbacks still remain.